Re: [PATCHv3 2/2] powerpc: implement arch_scale_smt_power for Power7
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: 2010-01-29 02:02:57
Also in:
lkml
On Thu, 2010-01-28 at 17:24 -0600, Joel Schopp wrote:
On Power7 processors running in SMT4 mode with 2, 3, or 4 idle threads there is performance benefit to idling the higher numbered threads in the core. This patch implements arch_scale_smt_power to dynamically update smt thread power in these idle cases in order to prefer threads 0,1 over threads 2,3 within a core.
Almost there :-) Joel, Peter, can you help me figure something out tho ? On machine that don't have SMT, I would like to avoid calling arch_scale_smt_power() at all if possible (in addition to not compiling it in if SMT is not enabled in .config). Now, I must say I'm utterly confused by how the domains are setup and I haven't quite managed to sort it out... it looks to me that SD_SHARE_CPUPOWER is always going to be set on all CPUs when the config option is set (though each CPU will have its own domain) or am I misguided ? IE. Is there any sense in having at least a fast exit path out of arch_scale_smt_power() for non-SMT CPUs ? Joel, can you look at compiling it out when SMT is not set ? We don't want to bloat SMP kernels for 32-bit non-SMT embedded platforms. Oh, and one minor nit:
quoted hunk ↗ jump to hunk
Signed-off-by: Joel Schopp <redacted> --- Version 2 addresses style and optimization, same basic functionality Version 3 adds a comment, resent due to mailing format error Index: linux-2.6.git/arch/powerpc/kernel/smp.c ===================================================================--- linux-2.6.git.orig/arch/powerpc/kernel/smp.c +++ linux-2.6.git/arch/powerpc/kernel/smp.c@@ -620,3 +620,59 @@ void __cpu_die(unsigned int cpu) smp_ops->cpu_die(cpu); } #endif
^^^ Please add the /* CONFIG_CPU_HOTPLUG */ (or whatever it is) that's missing after that #endif :-) Cheers, Ben.